1. Field of the Invention
This invention relates to a small neon lamp, a method of producing the neon lamp, and a system for producing the neon lamp.
2. Background Art
Small neon lamps are used chiefly as pilot lamps in camera stroboscopic flash units. FIG. 7 shows the structure and shape of a typical small neon lamp 100.
The neon lamp 100 is composed of a sealed glass bulb filled with neon gas, electrodes 2, 2 disposed inside the glass bulb, and leads 3, 3 connected to the electrodes 2, 2. The head portion 4 of the glass bulb is formed with a projecting tip portion 40. The projecting tip portion 40 is a vestige formed when, as explained later, a thin glass pipe portion is fused after charging the glass bulb with neon gas.
When the neon lamp is used as a pilot lamp, the projecting tip portion 40 is a nuisance because, for instance, it takes up extra installation space, makes emitted light hard to see when positioned in the line of sight, and is apt to break during installation.
Two methods have been developed for producing a flat-headed neon lamp without the projecting tip portion.
One method is substantially the same as the method used to produce subminiature electric lamps. In this method, two electrodes are fixed together by a glass bead and the result is inserted into an opening in a glass bulb of U-shaped cross-section, the glass bulb is evacuated of air and charged with a neon gas while taking care to prevent dropout of the bead-fixed electrodes, the glass bead is fused to the glass bulb, and superfluous glass cut away to obtain a lamp.
In the other method, two electrodes are sealed within one end of a glass tube and the result is fabricated into a bulb whose other end (head) is left open for evacuation of air and charging of neon gas. Next, in a vacuum apparatus, the bulb is evacuated and charged with neon gas, whereafter fabrication of the lamp is completed by using a carbon heater to fuse the head portion and seal the opening.
These methods of producing a neon lamp eliminate the problems caused by the presence of a projecting tip portion but have the following problems of their own:
1) As the DC current applied to a neon lamp fabricated by one of the foregoing methods rises, the point of discharge moves away from the center of the electrodes toward the tip. This adversely affects the lamp discharge characteristics.
2) In both methods, production cost is increased by the need to employ special equipment.
3) In the latter method, cost is increased because relatively expensive electric power is required to operate the carbon heater used to fuse the glass in the vacuum apparatus. Moreover, the fact that the glass tube has to be manually transferred to the vacuum apparatus after sealing the electrodes in the glass tube requires the method to be carried out as a time-consuming batch operation.
One object of the present invention is therefore to provide a neon lamp capable of preventing the unwanted discharge mentioned above.
Another object of the present invention is to provide a method of and a system for producing a flat-headed neon lamp capable of fully utilizing conventional production equipment without need for expensive special equipment.
In its first aspect, the present invention achieves these objects by providing a neon lamp comprising a sealed glass bulb disposing electrodes inside the glass bulb, and leads connected to the electrodes, the sealed glass bulb having a flat or lenticular head portion whose center region descends into the interior of the sealed glass bulb.
The neon lamp according to the first aspect of the invention effectively overcomes the problem regarding discharge characteristics mentioned above. Although the discharge starting voltage of a neon lamp depends almost entirely on the pressure of the neon gas and the distance between the electrodes, a DC-operated neon lamp such as a stroboscopic flash pilot lamp may, depending on the state of the electrodes and other factors, experience a shift in the discharge point away from the middle toward the tip of the electrodes as the applied DC voltage increases. This shift makes the characteristics of the lamp unstable.
When the center region of the glass head portion is formed to descend into the interior of the sealed glass bulb as in the first aspect of the invention, however, shifting of the discharge point and associated flicker are prevented and the characteristics of the neon lamp are stabilized.
In its second aspect, the present invention achieves the foregoing objects by providing a method of producing a neon lamp comprising a step of charging inert gas such as neon into a glass tube preinstalled with electrodes and leads at a head portion of the glass bulb, a step of sealing the glass tube to obtain a sealed glass bulb having a projecting tip portion, a step of removing excess glass of the projecting tip portion, and a step of shaping the projecting tip portion into a substantially flat or lenticular head portion.
The step of removing excess glass of the projecting tip portion is for adjusting the amount of descent when the head portion of the glass bulb is formed to descend into the interior of the sealed glass bulb.
In the production method according the present invention, the projecting tip portion is shaped after removal of excess glass. The head portion of the neon lamp can therefore be made substantially flat or lenticular and, in addition, can be shaped to descend inward by utilizing negative pressure generated inside the sealed glass bulb to suck the glass of the projecting tip portion inward.
In its third aspect, the present invention achieves the foregoing objects by providing a system for producing a neon lamp comprising a shaping head for accommodating a sealed glass bulb containing inert gas such as neon and having a projecting tip portion, with the projecting tip portion exposed outside the shaping head, a projecting tip cutter for removing excess glass of the projecting tip portion, and a head presser for shaping the projecting tip portion into a substantially flat or lenticular shape.
The system according to the present invention can be configured by combining an existing sealed glass bulb production apparatus with a shaper composed of a shaping head, a projecting tip cutter, and a head presser.
The system is therefore capable of producing both conventional neon lamps like that shown in FIG. 7 and neon lamps according to the present invention.